Adequate sexual function is a complex interaction of hormonal events and psychosocial relationships. The term xe2x80x9csexual dysfunctionxe2x80x9d generally includes any sexual dysfunction in an animal, preferably a mammal, more preferably a human. The animal can be male or female. Sexual dysfunction may include, for example, sexual desire disorders, sexual arousal disorders, orgasmic disorders and sexual pain disorders. Female sexual dysfunction refers to any female sexual dysfunction including, for example, sexual desire disorders, sexual arousal dysfunction, orgasmic dysfunction, sexual pain disorders, dyspareunia, and vaginismus. The female can be pre-menopausal or menopausal. Male sexual dysfunction refers to any male sexual dysfunction including, for example, male erectile dysfunction and impotence. There are four stages to sexual response as described in the International Journal of Gynecology and Obstetrics, 51(3): 26-77 (1995). The first stage of sexual response is desire. The second stage of sexual response is arousal. Both physical and emotional stimulation may lead to breast and genital vasodilation and clitoral engorgement (vasocongestion). In the female, dilation and engorgement of the blood vessels in the labia and tissue surrounding the vagina produce the xe2x80x9corgasmic platform,xe2x80x9d an area at the distal third of the vagina where blood becomes sequestered. Localized perivaginal swelling and vaginal lubrication make up the changes in this stage of sexual response. Subsequently, ballooning of the proximal portion of the vagina and elevation of the uterus occurs. In the male, vasodilation of the cavernosal arteries and closure of the venous channels that drain the penis produce an erection. The third stage of sexual response is orgasm, while the fourth stage is resolution. Interruption or absence of any of the stages of the sexual response cycle can result in sexual dysfunction. One study found that 35% of males and 42% of females reported some form of sexual dysfunction. Read et al, J. Public Health Med., 19(4): 387-391 (1997). In both pre-menopausal and menopausal females, sexual dysfunction can include, for example, sexual pain disorders, sexual desire disorders, sexual arousal dysfunction, orgasmic dysfunction, dyspareunia, and vaginismus. Sexual dysfunction can be caused, for example, by pregnancy, menopause, cancer, pelvic surgery, chronic medical illness or medications.
The vasculature, which serves erectile tissue in males and females, is similar. In particular, the arterial circulation of the erectile tissues of the genitalia derives from the common iliac artery which branches from the abdominal aorta. The common iliac artery bifurcates into the internal and external iliac arteries. The internal pudic artery arises from the smaller of two terminal branches of the anterior trunk of the internal iliac artery. In the female, the internal pudic artery branches into the superficial perineal artery, which supplies the labia pudenda. The internal pudic artery also branches into the artery of the bulb, which supplies the bulbi vestibuli, and the erectile tissue of the vagina. The artery of the corpus cavernosum, another branch of the internal pudic artery supplies the cavernous body of the clitoris. Still another branch of the internal pudic artery is the arteria dorsalis clitoridis, which supplies the dorsum of the clitoris and terminates in the glans and membranous folds surrounding the clitoris, which correspond to the prepuce of the male.
In the male, the internal pudic artery branches into the dorsal artery of the penis (which itself branches into a left and right branch) and the artery of the corpus cavernosum, all of which supply blood to the corpus cavernosum. The dorsal artery of the penis is analogous to the artery dorsalis clitoridis in the female, while the artery of the corpus cavernosum in the male is analogous to the artery of the same name in the female.
The male erectile response is regulated by the autonomic nervous system, which controls blood flow to the penis via the interaction of peripheral nerves associated with the arterial vessels in and around the corpus cavernosum. In the non-aroused or non-erect state, the arteries serving the corpus cavernosum are maintained in a relatively constricted state, thereby limiting the blood flow to the corpus cavernosum. In the aroused state, the smooth muscles associated with the arteries relax and blood flow to the corpus cavernosum greatly increases, causing expansion and rigidity of the penis. Smooth muscle contraction opens valves through which blood can flow from the corpus cavernosum into the extracavernosal veins. When the relevant smooth muscles relax, the valves close diminishing venous outflow from the corpus cavernosum. When accompanied by increased arterial blood flow into the corpus cavernosum, this results in engorgement of the corpus cavernosum and an erection.
While there are obvious differences in the sexual response between males and females, one common aspect of the sexual response is the erectile response. As described in U.S. Pat. No. 5,565,466, the disclosure of which is incorporated herein by reference in its entirety, the erectile response in both males and females is the result of engorgement of the erectile tissues of the genitalia with blood caused by the relaxation of smooth muscles in the arteries serving the genitalia.
Erectile dysfunction is a widespread disorder that is thought to affect about 10% to 15% percent of adult men. A number of causes of erectile insufficiency, in addition to anatomical deficiencies of the penis or scrotum that preclude an erection sufficient for vaginal penetration, have been identified. Causes of erectile dysfunction can be categorized as psychogenic, neurogenic, endocrinologic, drug-induced, or vasculogenic and in any individual suffering from erectile dysfunction there may be more than one cause.
Psychogenic impotence is often the result of anxiety or depression with no apparent somatic or organic impairment. Neurogenic impotence may arise from, for example, surgery or a pelvic injury, involving the nervous system affecting the penis. Erectile dysfunction, which is endocrinologic in origin, is most often associated with the disorders hypo- or hypergonadotropic hypogonadism and hyperprolactinemia.
Vasculogenic impotence is thought to be the most frequent cause of impotence accounting for approximately fifty percent of all cases of organic impotence. In these cases, the erectile dysfunction may be attributed to alterations in the flow of blood to and from the penis. Atherosclerotic or traumatic arterial occlusive disease to the arteries which supply blood to the penis can lead to a decrease in the rigidity of the erect penis as well as increase the time to achieving maximal erection. In still other cases, there is leakage from veins in the penis such that sufficient pressure for an erection can be neither obtained nor maintained.
There is also a high incidence of erectile insufficiency among diabetics, particularly those with insulin-dependent diabetes mellitus. Erectile dysfunction in diabetics is often classified as xe2x80x9cdiabetogenic,xe2x80x9d although the underlying dysfunction is usually neurogenic, but may be vasculogenic or neurogenic and vasculogenic. About half of diabetic males suffer from erectile insufficiency, and about half of the cases of neurogenic impotence are in diabetics.
Erectile insufficiency is sometimes a side effect of certain drugs, such as beta-antagonists that are administered to reduce blood pressure in persons suffering from hypertension, or drugs administered to treat depression or anxiety. Excessive alcohol consumption has also been linked to erectile insufficiency. These forms of erectile insufficiency may be regarded as a subset of neurogenic or psychogenic insufficiency.
A number of methods to treat impotence are available. These treatments include pharmacological treatments, surgery and, in cases of psychogenic dysfunction, psychological counseling is sometimes effective. Psychogenic impotence often can be cured by counseling coupled with a demonstration to the patient that he is capable of having a full erection by inducing such an erection from one to a few times in the patients. Reducing or eliminating such consumption sometimes cures insufficiency due to excessive alcohol consumption.
In the rare cases where the insufficiency is untreatable because of venous leakage, surgery can usually be used to repair the venous lesion and thereby either cure the insufficiency or, if there remains an erectile insufficiency after repair of the venous lesion, render the insufficiency amenable to treatment by pharmacological methods. Also, penile implants, which provide a mechanic means to produce an erection sufficient for vaginal penetration, are widely used to treat impotence. In recent years, implants have been used, especially in cases where pharmacological intervention is ineffective, which are usually cases of severe vasculogenic impotence. Treatment of impotence with penile implants, however, entails serious disadvantages. Such treatment requires surgery and necessitates total destruction of the erectile tissues of the penis, forever precluding normal erection.
Pharmacological methods of treatment are also available. Such methods, however, have not proven to be highly satisfactory or without potentially severe side effects. Papaverine is now widely used to treat impotence, although papaverine is ineffective in overcoming impotence due, at least in part, to severe atherosclerosis. Papaverine is effective in cases where the dysfunction is psychogenic or neurogenic and severe atherosclerosis is not involved. Injection of papaverine, a phosphodiesterase inhibitor and a smooth muscle relaxant, or phenoxybenzarnine, a non-specific antagonist and hypotensive, into corpus cavernosum has been found to cause an erection sufficient for vaginal penetration, however, these treatments are not without the serious and often painful side effect of priapism. Also, in cases where severe atherosclerosis is not a cause of the dysfunction, intracavernosal injection of phentolamine, an xcex1-adrenergic antagonist, causes an erection sufficient for vaginal penetration. The resulting erection is one of significantly shorter duration than that induced by intracavernosal injection of papaverine or phenoxybenzamine and often times is of such short duration that satisfactory sexual relations are difficult or impossible. As an alternative or, in some cases an adjunct to phosphodiesterase inhibition or a-adrenergic blockade for the treatment of erectile dysfunction, prostaglandin E1 (PGE1) has been administered via intracavernosal injection. A major side effect frequently associated with intracorporally delivered PGE1 is penile pain and burning.